Apparatus for continuous conversion of starch



Oct 24, 1957 3,348,972

APPARATUS FOR cou'rmuous CONVERSION OF STARGH 5. G. TAYLOR OriginalFiled March 9, 1961 S mm m H m wm F m w m m M w E Y B 3 G H WM UnitedStates Patent 3,348,972 APPARATUS FOR CONTINUOUS CONVERSION OF STARCHGerwin G. Taylor, Flossmoor, lll., assignor to American Maize-Products(Iompany, a corporation of Maine Original application Mar. 9, 1961, Ser.No. 94,515, now

Patent No. 3,169,083, dated Feb. 9, 1965. Divided and this applicationFeb. 19, 1964, Ser. No. 345,929

5 Claims. (Cl. 127-48) This application is a division of co-pendingapplication Serial No. 94,515, filed March 9, 1961, now US. Patent No.3,169,083 granted February 9, 1965.

This invention relates to a method and apparatus for the continuousconversion of starch.

In many prior art continuous processes for the conversion of starch intodextrose and related intermediate products an acid catalyzed aqueousslurry of starch is customarily heated to reaction temperature undersuper atmospheric pressures by injection of live steam therein and theslurry is held under such reaction conditions in a closed vessel knownas a converter for a sufficient period of time until the desired degreeof hydrolytic break-down of the starch into sugars has been obtained.Thereafter, the reaction liquor is flashed into a suitable vessel atatmospheric pressure, volatile residues are removed and the remainingsugary syrup is neutralized.

The holding time of starch slurry in the converter is a critical part ofthis process. All other reaction variables being constant, the degree ofconversion, known in the trade as the dextrose equivalent (D.E.),increases as the holding time is lengthened but long holding times leadto the formation of objectionable discoloration in the conversionproduct and should be minimized. Since the starch slurry movescontinuously through the converter, the holding time is a function ofthe rate of flow and the volume capacity of the converter and one of theserious problems in the prior art processes has been the failure toachieve a continuous uniform flow through the converter. As a result thestarch slurry in part tends to be overcooked and undercooked so that asa practical matter the final DB. of the conversion product is diflicultto control and subject to wide variation.

We have now devised an apparatus for use as a converter for the starchslurry which makes it possible to achieve completely uniform flow of theslurry and exceptional control over the DE. value of the conversionproduct. In the converter of our invention there is no tendency foraxial intermixing of portions of the starch slurry along the length ofthe converter as may be caused by turbulent flow or by slippage ofconcentric tubes of slurry from the frictional drag of the insideconverter wall and in accordance with the present invention a crosssectional area of the slurry is caused to move uniformly through theconverter so that holding time may be controlled to give a final productwith DB. held within narrow well defined limits.

The converter comprises a cylindrical vessel having at least one paddleblade extending along the length of the vessel. The blade is attached toa rotatable central shaft by means of horizontal arms and the spacing ofthe blade gives a slight clearance between the inside wall of the vesseland the outer edge of the blade.

As the mixture of steam and starch slurry under reaction temperature andpressure enters this vessel, the central shaft and the blade is rotatedat controlled speed sufficient to disrupt the laminar flow pattern ofthe slurry in the area adjacent the inside wall of the vessel. In theabsence of agitation there is a drag exerted on the outer concentricportions of the slurry which slows the movement of these portions ascompared to the central portion 3,348,972 Patented Oct. 24, 1967 so thatthe flow pattern is laminar, that is, an increasing relative slippagebetween concentric tubes of slurry from the outer to the inner portionsof the slurry. The agitation provided in the converter of this inventiontends to break up this laminar flow pattern and prevent the centralportion of the slurry from moving through the converter at a greaterspeed than the outer portion. As a result a cross sectional unit volumeof slurry moves continuously through the converter in uniform mannerover the proper holding time and the slurry is converted to asubstantially uniform D.E. product.

As mentioned hereinabove the converter has at least one blade positionedadjacent the inside wall of the converter to give a slight clearancetherewith. This clearance need not be uniform throughout, that is, theradial distance between the outermost edge of the blade and the insidewall need not be the same throughout the length of the blade. The bladeedge can have'serrations or the blade itself may be angled away from avertical position in which case it is also suitably curved to permitrotation in the cylindrical converter. In the preferred form ofconverter illustrated in the drawings there are two blades spaceddiametrically opposite each other and parallel to the vertical axis ofthe converter. This construction has proven to be quite satisfactory butit is recognized that other specific forms of blades and more than oneor two blades may also be employed.

As to control speed of rotation, in working with a converter of the typeshown in the drawings having a diameter of one foot, it has been foundthat the peripheral speeds of rotation of the blades should becontrolled preferably at about 15 to about 53 feet per minute. The termperipheral speed of rotation means the angular y velocity of the bladerelative to the stationary converter wall as the blade is rotating. Theabove specified range is preferred but peripheral speeds of rotation ofabout 10 to about 100 feet/min. may be employed with satisfactoryresults. Also, depending on the physical character istics of theselected converter such as diameter, shape, texture of interior wallsurface, number of blades employed and the like, speeds of rotationoutside those specified herein may be employed to achieve equivalentresults of breaking up the laminar flow pattern of the starch slurrywithout departing from the spirit and scope of the invention. In allcases the selected speed of rotation should not cause axial intermixingof the slurry during flow through the converter.

Preferably the walls of the converter are insulated so that the totalheat will be contained in the slurry during the holding time. The rateof flow of the slurry is correlated with the actual dimensions of theconverter and the level of fluid in the converter in order to establishthe holding time required for the particular D.E. product beingmanufactured. For this purpose the converter is equipped withconventional automatic fluid level controls which will maintain thefluid level at any desired point. For example, if the rate of flow ofthe slurry is 12 gal./ min. and the volume capacity of the converter is144 gal, the average holding time for a unit volume of slurry movingthrough the converter when completely filled would be about 12 minutes.By maintaining the converter only about full, the holding time will bereduced to 10 minutes for the same slurry flow rate.

It is possible with the converter of this invention to form starchconversion products having D.E. values from essentially 0, i.e. cookedstarch, to as high as 95. It is also possible to convert starch slurriesof a density anywhere between 0 B and 24 B or more and low D.E. syrupscan be upgraded to syrups having higher D.E. values.

For a better understanding of further details of this inventionreference will be made to the accompanying and Koerting continuousheater, into which steam under super atmospheric pressures is fed intothe starch slurry by the steam line 16. A connecting line 18 runs fromthe heater and empties into the top of the cylindrical vessel orconverter 20. The converter is equipped with a centrally located shaft22 which is connected to the shaft of a driving mechanism 24. Tworectangular paddle blades 26 are connected to the central shaft by meansof arms 28. As shown in FIGS. 1 and 2 the blades extend substantiallythroughout the length of the vessel 20, are parallel therewith and arepositioned diametrically opposite each other. There is a slightclearance between the outermost longitudinal end faces 30 of the bladesand the inside wall 32 of the vessel. The vessel is equipped with anautomatic fluid level control 34 of conventional type and the walls ofthe vessel are provided with insulation 36 to prevent loss of heat.

The bottom portion of the vessel is preferably cone shaped and leads tooutlet line 38. The outlet line 38 connects to one side of a discharge'valve 40. The other side of the valve is connected to line 42 whichempties into a conventional cyclone type liquid-vapor separator 44. Theseparator has a product discharge line 46 at the bottom thereof and avent line 48 for flashing off volatile vapors. Between the dischargevalve and the separator, line 42 is tapped with line 50 leading from thepump 52 which is connected to a holding tank 54. From the heater 12 upto the discharge valve, 40, the equipment is reinforced to withstandsuper atmospheric pressures. Except for the converter, the rest of theapparatus described hereinabove is well known conventional equipmentreadily available on the open market and a detailed description of suchequipment is not deemed necessary as it forms no part of our invention.

The dimensions of the specific form of converter illustrated in thedrawings are a diameter of one foot and a length of twelve feet in thecylindrical vessel. The paddle blades are /4 inch thick and two incheswide. They are attached to a 1 /2 inch diameter round center shaft bymeans of the three horizontal arms which are 4 inch diameter round bars.The position of the blades is such that there is a clearance ofapproximately /4 inch between the outermost edges of the blades and theinside wall of the tank.

In the operation of the above described apparatus an aqueous slurry ofstarch catalyzed in conventional manner with an acid catalyst such ashydrochloric, sulfuric or phosphoric acid, is continuously pumped intothe heater 12. Super atmospheric steam passing through the steam line 16and jet 14 violently commingles with the slurry whereby the temperatureof the slurry is substantially instantaneously raised to reactiontemperatures between about 240 F. to 325 F. under super atmosphericpressures. The slurry then passes into converter 20, the paddle blades26 of which are turning at a controlled speed as described hereinabove.

As the starch slurry moves down through the converter the paddle bladesbreak up the laminar flow pattern of the portion of the slurry which isnear the inside wall of the converter so that a unit volume of slurryfalls through the converter in completely uniform manner. The automaticlevel control 34 maintains the converter filled to any desired level ofslurry and this, in combination with control of the rate of flow of theslurry, provides a means for holding the slurry under the reactionconditions for con version over holding times of about 1 to about 150minutes. After reaching the bottom of the converter the hydrolyzedslurry passes through line 38 to the valve 40 where it is flashed intoline 42 at atmospheric orslightly higher pressure. The acid catalyst inthe conversion product is continuously neutralized in conventionalmanner with aqueous alkali which is pumped from the holding tank 54 upthrough line 50 and into the stream of conversion product flowingthrough line 42. The neutralized liquid conversion product then passesinto the separator 44 where volatile residues are flashed off and theproduct is discharged through line 46. The volatile residues consistprimarily of low pressure steam vapors which may be utilized to preheatthe feed starch slurry, other process liquors, or water.

From the foregoing description it is obvious that the dimensions of theapparatus and the various reaction.

factors of the process are variable within wide limits to suit the needsin each particular case. In general, conversion products up to DE. aresatisfactorily made with starch slurriesof about 23 to 24 B. Forproducts of higher than 80 DE. preferably the density of the starchslurry is about 10 to 15 Be. In order to give an idea of the possiblesets of values that may be used in producing various D.E. conversionproducts the following examples are given. The examples are given interms of operation of the converter illustrated in the drawings.

Typical operating conditions to produce a 42 DE. syrup are:

Density of starch slurry B 3.0 Amount of 20 B hydrochloric acid, vol.percent 0.21 Steam pressure p. s.i Slurryflow rate gal./min 2 Conversiontemperature F 282 Pressure in converter p.s.i 36 Holding time min 10Peripheral speed of rotation ft./min 40. Example 3 Typical operatingconditions to produce a 54 DE. syrup are:

Density of starch slurry B 23.0 Amount of 20 B hydrochloric acid, vol.percent 0.21 Steam pressure p.s.i Slurry flow rate gal./min 12Conversion temperature F 291 Pressure in converter p.s.i 44 Holding timemin 10 Peripheral speed of rotation ft./min 30 Example 4 Typicaloperating conditions to produce a 92 DE. syrup are:

Density of starch slurry B 12.0 Amount of 20 B hydrochloric acid, vol.percent 0.32 Steam pressure p.s.i 125 Slurry flow rate gal./min 6Conversion temperature F 310 Pressure in converter p.s.i 63 Holding timemin 24 Peripheral speed of rotation ft./min 15 Although the converterhas now been specifically described in connection with two spaced paddleblades, as mentioned hereinabove, it is possible to use more than twoblades spaced equidistant from each other around the inside wall of theconverter. In general if the diameter of the converter is substantiallygreater than one foot it is recommended that more than two paddle bladesbe employed and the blades be rotated at peripheral speeds slower thanthose used in the smaller diameter converter in duplicating a DB productmade with the smaller diameter converter. In all cases it is importantthat the maximum speed of rotation not disrupt the flow of slurry to thepoint of causing turbulence or axial mixing which reduces the uniformityof the DE. value of the conversion product and therefore, is highlyundesirable.

One modification of the invention is shown in FIG. 3- The conduit .38leads to a second vessel 20A similar in construction to the first vessel20 and the starch conversion product is discharged here from an outletport adjacent the top of the second vessel. This modification willpermit longer holding times at the same flow rate or higher flow ratesat the same holding time or many additional variations of holding timesand fiow rates without the converter being excessively long.

It will be understood that it is intended to cover all changes andmodifications of the preferred embodiment of the invention herein chosenfor the purpose of illustration which do not depart from the spirit andscope of the invention.

What is claimed is:

1. An apparatus for a continuous process of converting acid catalyzedstarch slurries into dextrose and related intermediate products bysubjecting said slurries to heat and pressure comprising a closedcylindrical ves- 35 sel having an inlet port, an outlet port and acentral rotatable shaft, at least one paddle blade attached to saidshaft, said paddle blade extending substantially throughout the vesseland being positioned closely adja- 2. An apparatus in accordance withclaim 1 in which the walls of the vessel are provided with insulationagainst loss of heat.

3. An apparatus in accordance with claim 1 in which 5 the walls of thevessel are reinforced to withstand super atmospheric pressures.

4. An apparatus in accordance with claim 1 which includes tworectangular paddle blades spaced diametrically apart from each other.

5. An apparatus for a continuous process of converting acid catalyzedstarch slurries into dextrose and related intermediate products bysubjecting said slurries to heat and pressure comprising a closedcylindrical vessel having an inlet port and an outlet port for thecontinuous flow of starch slurry through said vessel, means for feedingslurry through the inlet port to cause the slurry to flow through thevessel and be discharged from the outlet port, at least one paddle bladeextending substantially throughout the length of the vessel which paddleblade is positioned closely adjacent the inside wall of the vessel toprovide a slight clearance space therebetween, a shaft for mounting thepaddle blade, means for rotating the shaft and blade at a controlledrate of speed comprising an angular peripheral speed for said bladeequivalent to 10 to 100 feet per minute for a vessel one foot indiameter, means for maintaining the level of fluid slurry in said vesselat a predetermined height, and pressure regulating means associated withthe outlet port to control the pressure in the vessel and maintain theslurry under superatmospheric pressure therein.

References Cited UNITED STATES PATENTS 2/1921 Scott 259-401 cent theinside Wall of the vessel to provide a slight clearance spacetherebetween, means for rotating said paddle blade at angular peripheralspeeds equivalent to 10 to 100 feet per minute for a vessel one foot indiameter, and means for maintaining the level of fluid slurry in saidvessel at a predetermined height.

JOSEPH SCOVRONEK, Primary Examiner. MORRIS O. WOLK, Examiner.

E. G. WHITBY, Assistant Examiner.

1. AN APPARATUS FOR A CONTINUOUS PROCESS OF CONVERTING ACID CATALYZEDSTARCH SLURRIES INTO DEXTROSE AND RELATED INTERMEDIATE PRODUCTS BYSUBJECTING SAID SLURRIES TO HEAT AND PRESSURE COMPRISING A CLOSEDCYLINDRICAL VESSEL HAVING AN INLET PORT, AN OUTLET PORT AND A CENTRALROTATABLE SHAFT, AT LEAST ONE PADDLE BLADE ATTACHED TO SAID SHAFT, SAIDPADDLE BLADE EXTENDING SUBSTANTIALLY THROUGHOUT THE VESSEL AND BEINGPOSITIONED CLOSELY ADJACENT THE INSIDE WALL OF THE VESSEL TO PROVIDE ASLIGHT CLEARANCE SPACE THEREBETWEEN, MEANS FOR ROTATING SAID PADDLEBLADE AT ANGULAR PERIPHERAL SPEEDS EQUIVALENT TO 10 TO 100 FEET PERMINUTE FOR A VESSEL ONE FOOT IN DIAMETER, AND MEANS FOR MAINTAINING THELEVEL OF FLUID SLURRY IN SAID VESSEL AT A PREDETERMINED HEIGHT.